Manufacturers of semiconductor devices, to increase the production capacity of their factories, work to maximize device yield per wafer. That is, their goal is to maximize the number of working devices built on each substrate wafer. Each step in the manufacturing process must be made to occur uniformly at locations across the surface of the substrate, thus allowing for uniform device construction.
Ideally, a substrate used in the formation of semiconductor devices is substantially flat and remains so as it is altered throughout the device formation process. However, it is common in the modern processing environment for a substrate to arrive at a processing step in a state of being, for example, bent, bowed, rippled, warped, or otherwise deformed. This deviation from planarity may occur because the various layers processed into or onto the original substrate have differing compositions. Thus, they react differently to the processing steps, expanding or contracting by various amounts. The layers can pull against each other, causing the substrate to deform. This prevents uniform film deposition, polishing, and lithographic exposure across the substrate surface.
Some modern vacuum chucks attempt to address this problem by pulling the raised portions of the substrate down against the chuck using vacuum pressure drawn through an array of holes in the surface of the chuck. In some cases, attempts are made to “smooth” deformed substrates over the chuck's surface by successively pulling adjacent sections of the substrate down. However, the substrate is sometimes too deformed for adequate vacuum pressure to form between it and the chuck, preventing the substrate from being secured to the chuck.
The prior art also includes clamps that secure a substrate for manipulation during processing, but these clamps are configured for flat and somewhat rigid substrates. They do not address the problem of deformation seen especially in thin substrates which typically lack rigidity.
Accordingly, there is a need for a substrate handling mechanism which is able to accept a warped substrate and make it lay flat against an underlying surface for processing.